Through patent document ES 2122490 a mesh bag is known comprising a tubular mesh casing having, longitudinally arranged and on the outer side, a handle of resistant synthetic material welded at its ends to the ends of said tubular casing coinciding with the weldings themselves for sealing of the casing.
To assist in sealing the casing, it comprises pieces of plastic band located on the ends and outside the tubular mesh, opposite the ends of the strap that acts as a handle, such that the sealing of said casing is sought by juxtaposing and mutually joining the ends of the handle and these pieces of band with interposition of the mesh forming the casing at each end of said casing.
In some cases when gripping the bag by the handle or when handling the bags during storage or transport, the weight of the products housed in the casing can cause a twisting effect therein such that it can prevent the bag from being exposed in a satisfactory way or that carrying it may not be as comfortable as expected even though the bag has a handle.
Similarly, when the bag is gripped by the handle, the mesh material must support the entire weight of the product housed inside, so that the thickness and size of the mesh must be selected correctly ensuring that it will hold without breaking. Furthermore, the joint between the ends of the strap forming the handle and the tubular mesh must be carried out such as to ensure that said joint will withstand or resist the weight of the products. All of the foregoing means that certain features of the bag must be excessively oversized.
A known type of machine for manufacturing mesh bags based on the supply of a continuous tubular mesh is one which comprises a station for producing bags with an expansion device or expander core, arranged in floating and vertical manner on the inside of the tubular mesh and supported by at least one pair of rotating rollers outside the mesh, the shafts of which are integral with the machine.
This expansion device is configured to cooperate with welding groups arranged one on each side of the expansion device, and which, when actuated, ensure the joining of the expanded tubular mesh as it passes through the expansion device and a sheet material which is placed outside the tubular mesh.
Conventionally, the station for producing bags is further equipped with a sealing device of the tubular mesh, gathering and joining together the wall thereof through thermo welding or by other means. Usually, the sealing of the tubular mesh is made to coincide with a portion of the tubular mesh having sheet material attached, on one or both sides thereof, in order to reinforce the sealing and prevent tearing of the mesh at this point. Also conventionally, the station for producing bags is equipped with a cutting device, downside of the sealing device, which transversally cuts the mesh immediately below the sealing area in order to individualize a bag of continuous mesh, bag that remains open at the top but closed at the bottom through previous actuation of the sealing device.
An example of a station for producing bags having these characteristics is described in patent document ES2188389.
The individualized bag is transferred to other stations of the machine, where it will be filled and subsequently sealed by gathering and joining together the walls of the bag in the vicinity of its upper opening.
The type of bags to be produced may vary according to whether the sheet material is applied only on one side or on both sides of the tubular mesh, in the station for producing bags. Similarly, different bags can also be produced depending on whether the sheet material is joined to the body of the mesh along the entire length of a bag or only coinciding with the bottom thereof and the upper opening.
Each of these alternatives requires the use of different welding groups. To that end, in order for a station for producing bags to be sufficiently versatile and capable of making different types of bags, it is possible to equip the station for producing bags with an upper welding group and a lower welding group, of a different typology, and enable the station for producing bags so that the expansion device can be easily replaced, according to whether the latter should cooperate with the upper welding group in order to manufacture a version of the bags, or with the lower welding group in order to manufacture other versions of the bags.
In some cases, the bags, such as those that are object of the present invention, do not necessarily have to be symmetrical, that is, the relationship between the laminar sheet and the tubular mesh may be different on either side of the tubular mesh. Thus, bags with interesting added benefits can be obtained.
The production of these versions of the bags in a station for producing bags as described above is not well resolved because it requires the use of an upper welding group arranged on one side of the tubular mesh and a lower welding group arranged on the opposite side of the tubular mesh, requiring the simultaneous use of two expansion devices when the station is only able to support one of these at a time.
The first objective of the invention is a station for producing bags capable of overcoming this drawback.
It is also an objective of the invention to maintain the production rate of the station for producing bags even when the bag being produced is of the type that requires operating with both welding groups at different levels.